I have a Rivarossi 0-6-0T that did the same thing as yours. Rivarossi is basically out of business and Hornby (owners of said company) really didn't want to fool with the locomotive. I sent it off to a repair facility in the U.S. and they discovered the drivers were "out of quarter" (ie. both connecting rods were down where they should be opposed). The repair place put the offending driver in the correct position and 'secured' (epoxied?) the axle - such that it won't move again. Problem solved. Hope this helps...check the position of those connecting rods.